Mercury--cadmium--telluride (Hg.sub.(1-x) Cd.sub.x Te, where x ranges from approximately zero to 1.0 and has typical values ranging from 0.2 to 0.4) photodiodes are typically fabricated as two dimensional arrays and include a layer of passivation applied to an upper surface of the array, the passivation layer comprising low-temperature photochemical SiO.sub.2, evaporated ZnS, or anodically grown CdS. While suitable for some imaging applications it has been found that during certain subsequent processing steps which involve the array, such as a 100.degree. C., high vacuum bake cycle required to outgas a vacuum Dewar which houses the photodiode array, that such a conventional passivation layer may be disadvantageous. For example, there has been observed a degradation in critical performance parameters such as leakage current, quantum efficiency, noise (especially at low frequencies), spectral response, and optical area. This degradation is especially evident in long-wavelength detectors where changes in surface potential approaches the bandgap energy. Porosity of the passivation layer and lack of adhesion to the underlying HgCdTe surface are also common problems observed with the aforedescribed conventional passivation layers.
Furthermore, inasmuch as these conventional passivation materials form no more than a coating upon the HgCdTe surface, control over the energy levels at the HgCdTe/passivation interface is difficult or impossible to achieve. A limitation of such conventional coatings is that it is necessary to both create and maintain flatband conditions at the HgCdTe/passivation interface if the array is to maintain a desired level of performance parameters, especially during and after high temperature processing and storage.